1. Field of the Invention
The invention relates to an apparatus and method for automatically controlling loads imposed on an engine while operating, and is particulary adapted for, but not limited to, controlling load on an engine powering a controllable pitch propeller as used in marine applications.
2. Prior Art
Apart from light recreational marine craft, most commercial marine power vessels use a governor to control engine speed, and often power a controllable pitch propeller. Engine overloading can still occur due to operator error or adverse weather conditions and automatic load control or overload prevention systems have been designed to reduce loads on the engines. Some prior art load control systems are characterized by a slow response to an overload situation, and sometimes a "hunting" condition can arise between the automatic load control and the pitch control unit so that loading on the engine fluctuates between upper and lower limits producing erratic running of the engine. To the inventor's knowledge, prior art load control devices using pneumatic components have been relatively unsuccessful due to inaccuracy of control. Hydraulic devices have been characterized by slow response, and often exhibit hunting tendencies. While electronic devices have been relatively successful, and can be designed for a high degree of accuracy, they are costly and characterized by complex electronics which require servicing by specialised personnel, which are often not easily available on a marine vessel. Also, it can be difficult to protect sensitive electronic components from the harsh environment of marine vessels. Consequently, marine load control devices using complex electronics can be difficult to maintain, and when failure occurs, inexperienced on-board personnel can have difficulty in solving maintenance problems in isolated situations which can occur at sea.